#include <iostream>
#include <fstream>
//#include <bits/stdc++.h>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int n, nr_prime;
bool sir[2000001];

int main() {
    fin >> n;
    sir[1] = 1;
    for (int i = 2; i <= n; ++i) {
        if (sir[i] == 0) {
            ++nr_prime;

            if (i * i <= n) {
                for (int j = i + i; j <= n; j = j + i) {
                    sir[j] = 1;
                }
            }
        }
    }

    fout << nr_prime;

    return 0;
}